1. Field of the Invention
The present invention relates to a two-dimensional positioning device, and more specifically to such a device which includes a plurality of magnetic fields arranged two-dimensionally and a plurality of coil sets placed in the magnetic fields in order to control the position of a loading table or the like in the two dimensions, and still more specifically to such a device which finds useful applications in extremely accurate positioning of, for example, a semiconductor substrate during a manufacturing process. The present invention utilizes a phenomenon that a force is experienced by a current-carrying wire in a magnetic field.
2. Description of the Prior Art
In order to precisely position a loading table or the like in two dimensions, it is a common practice to use two driving means for driving the loading table in the two directions along the X and Y orthogonal coordinate axes, respectively. As such a driving means, a stepping motor or a rotary type D.C. servo motor has been utilized, wherein the rotary motion of the driving means is converted to linear motion by a feed screw or the like.
Such a driving means, however, is found to have difficulties in providing the loading table with fine displacement control of one micron meter or less. If an extremely fine displacement is required, then the screw pitches have to be made very fine, resulting in undesirable decreases of the driving speed. In order to achieve speedy, fine positionings of the loading table, a driving device has been proposed which includes two separate structures, one for coarse and the other for fine displacements. This prior art however is complicated and expensive. Further, the above-mentioned prior art has another problem in that two guides are required for limiting the displacements of the loading table in directions other than the intended X and Y directions.
B. A. Sawyer disclosed a two-axis magnetic system for driving chart plotters and other devices, entitled "Magnetic Positioning Device", in U.S. Pat. No. 3,376,578. This device however utilizes stepping motor technology, and hence is different in basic principle from the present invention.
On the other hand, there have been recent developments in D.C. linear motors, each of which is applicable to precise, speedy positionings of the loading table in one direction. However, in the case where D.C. linear motors are applied to two-dimensional positioning devices, two D.C. linear motors and two guide rails are required and hence the device is complicated in structure and expensive as described with the aforementioned prior art.
In an effort to solve the prior art difficulties, the inventor of the present invention has proposed improved positioning devices, which have been disclosed in Japanese patent applications Nos. 57-56344 and 57-57848.
Applications corresponding to Japanese applications Nos. 57-56344 and 57-57848 were filed in the United States (U.S. Pat. Nos. 4,536,278 and 4,555,650 respectively) claiming convention priorities. The devices in these applications, however, require some improvements because of a large number of coils and/or complicated control circuitry.